Pressurized air is among the more common cooling mediums used to cool various components in gas turbine engines. Generally in such systems, compressed air is drawn from the combustor shell and traverses a closed loop cooling system in which the air cools components of the turbine engine, e.g., the vanes, the blades and the combustors. Typically, the air is first filtered and cooled before its use as a coolant. After being cooled, the air is directed to the components to be cooled, and then the air is returned to the discharge of the compressor or the combustor shell of the gas turbine engine.
In such a closed loop system, the cooling air must be sufficiently pressurized in order to re-enter the combustor shell or mix with the air discharged from the compressor. Unfortunately, within the cooling circuit, the air generally experiences a pressure loss. This pressure loss is caused by the resistance of bends, orifices and other obstructions. To overcome these pressure drops and increase the pressure of the cooling medium to approximately that of the combustor shell or the discharge of the compressor, the air coolant, in some applications, is routed out of the turbine engine to an external compressor before it is returned to the combustion turbine and eventually the combustor shell. In the external compressor, the air coolant may be compressed about 60 PSI. Significantly, external compressors are expensive components, with costs in the $300,000 range. Other costs are associated with the use of external compressors, e.g., back up compressors, piping, operation, maintenance, floor space and the like. Applicants have recognized that a turbine engine that internally provides the pressurization required for the air coolant to reenter the combustor shell would eliminate the need for external compressors, thereby providing substantial economic benefits.
Thus, there is a need for pressure changing mechanisms that function within turbines and compress the cooling medium and thereby eliminate the need for external compressors. There is also a need for improved systems and methods for using the pressure reducing mechanisms that operate within turbines.